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MISCELLANEOUS PUBLICATION NO. 1065, U.S. DEPARTMENT OF AGRICULTURE 



vines can spread the infection in a few plants to 

 a whole field. Thus, proper cultural and harvesting 

 practices become important in disease control. 



Clubroot can be a serious disease of cabbage. 

 However, studies have shown that it can largely 

 be kept in abeyance by maintaining the soil reac- 

 tion close to neutral or slightly alkaline by liming. 



Potato scab requires the opposite treatment for 

 control from that indicated for cabbage clubroot. 

 Potato scab is kept in abeyance if the pH of the 

 soil is maintained below 5.2. 



The need to use chemical fungicides is sometimes 

 avoided by eliminating the alternate host of a 

 plant disease. The fungus causing the cedar rust of 

 apples must alternate its life cycle between para- 

 sitism on pome fruits such as apples, crabapples, 

 quinces, hawthorn, serviceberry, and the overwin- 

 tering hosts of several species of juniper. This 

 cedar rust in apple orchards can be largely con- 

 trolled by eliminating appropriate species of cedar 

 within a mile or so of the orchard. 



Stem rusts of wheat and other cereals have 

 caused tremendous damage in grain production in 

 the United States. An important alternate host is 

 the stem rusts for the common barberry. An exten- 

 sive program of eliminating wild barberries in the 

 wheat-growing areas of the United States has done 

 much to eliminate sources of infection for stem 

 rusts. 



White pine blister rust became a serious menace 

 to white pines in the United States during the first 

 quarter of this century. The disease organism must 

 have alternate hosts such as provided by goose- 

 berries and currants. An extensive program of 

 eliminating the susceptible species of alternate 

 hosts has done much to hold in abeyance the threat 

 of white pine blister rust. 



White pine blister rust is also attacked by an- 

 other approach to biological control. It has been 

 found that the hyperparasite Tuberculina maxima 

 inactivates many of the cankers formed from in- 

 fection over white pine blister rust but not enough 

 to provide effective control of the disease. Research 

 has also shown that certain fungi compete well 

 with oak wilt fungus in the bark of killed trees or 

 with the disease agent Fomes annosus in old pine 

 stumps and roots. Research is underway towards 

 finding how to stimulate the protective organisms. 



Plant breeding and selection has long been an 

 effective approach towards developing strains of 

 economic plants that would avoid the ravages of 



plant diseases without the use of chemical sprays 

 and dusts. Mildew-resistant cantaloups have been 

 developed. Wilt-resistant varieties of watermelons 

 have been produced. Sugar beets resistant to leaf- 

 spot have been developed. These are just a few 

 examples of plant diseases that would normally be 

 controlled by the fungicides if the plant did not 

 carry disease resistance. There are a tremendous 

 number of examples of plant breeding for disease 

 resistance wherein use of f ungicides was not feas- 

 ible and thus resistance of the crop plant was 

 virtually the only hope; for example, use of fungi- 

 cides in forests is of questionable economic feasi- 

 bility. Great progress has been made in research 

 towards eliminating the need for such chemicals 

 in the forest by developing hybrids of forest trees 

 that are immune or highly resistant to white pine 

 blister rust, fusiform rust, brown spot, littleleaf, 

 mimosa wilt, and chestnut blight. 



In fact, one could summarize by saying that the 

 contributions of agricultural and forestry research 

 towards controlling ravaging diseases without use 

 of chemicals has been one of the great contributions 

 of all research endeavor. 



Socioeconomic Evaluation 



The solution of waste disposal problems lies in 

 part outside the influence of the market system. 

 The price system works effectively for many of the 

 quantitative aspects ; however, it is difficult to at- 

 tach monetary significance to esthetic values which 

 are diminished by offensive odors or unsightly sur- 

 roundings. Despite these difficulties, it is essential 

 to consider esthetics when attempting to answer 

 questions such as: What level of waste treatment 

 do we want? How much can we afford to spend? 

 How much are we willing to pay for specific levels 

 of quality improvement? 



The analyses of alternative systems of alleviat- 

 ing waste problems are seriously hampered by the 

 general lack of information. A number of studies 

 are underway at State agricultural experiment sta- 

 tions and within the U.S. Department of Agricul- 

 ture. These studies will enhance the decision- 

 making process and contribute to the optimal eco- 

 nomic and social solutions to waste problems. These 

 studies are related to pesticides, water quality, 

 plant nutrients, and organic wastes. 



